The present invention relates to a magnetic resonance imaging apparatus for generating a magnetic resonance signal (MR signal) by applying a gradient field pulse and high-frequency magnetic field pulse to an object to be examined which is placed in a homogeneous static field, and generating a magnetic resonance image (MR image) on the basis of this MR signal.
In general, a magnetic resonance imaging apparatus of this type includes a static field magnet for generating a static field, a gradient field coil for generating a gradient field, and an RF coil for generating a high-frequency (RF) magnetic field pulse. An object to be examined is placed in the static field formed by the static field magnet. A gradient field pulse and RF magnetic field pulse are applied to this object in accordance with an arbitrarily selected pulse sequence. As a consequence, an MR signal is generated from the object. This MR signal is received via the RF coil. An MR image is reconstructed on the basis of the received MR signal.
In the recent technical field of magnetic resonance imaging apparatuses, with improvements in fast imaging technology, research and development have been vigorously carried out. MRI fast imaging requires fast switching of a gradient field and an increase in strength. For this reason, the gradient field coil vibrates. The vibrations cause noise. This noise sometimes reaches 100 db(A) or higher. This makes it necessary for an object to wear earplugs or headphones.
A typical measure against noise is to house a gradient field coil in a sealed vessel, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 63-246146, U.S. Pat. No. 5,793,210, and Jpn. Pat. Appln. KOKAI Publication No. 10-118043. The sealed vessel is evacuated to a nearly vacuum to suppress air-born propagation of noise.
Another typical measure against noise is to support a gradient field coil by a damper. This suppresses solid-born propagation of the vibrations of the gradient field coil to the sealed vessel and other parts.
Noise can be reduced to a certain degree by such measures against noise. However, it is impossible to further reduce the noise. This is because it is assumed that the gradient field coil is not the only noise source.